One process of constructing precast concrete slabs utilizes a fixed casting bed and a movable extruder which moves along tracks positioned longitudinally of the bed to extrude a relatively stiff mix of concrete onto the bed.
Prior to extruding the concrete onto the casting bed it is generally necessary to perform several preparatory operations. For example, it is desirable to spray the casting bed with a release agent to facilitate removal of the hardened concrete slab. Prestressing strands are usually used in slabs of this type and the strands must first be laid in the bed before they are anchored and prestressed.
Very often various types of production hardware, such as bolt sockets, anchors, plates and other accessories are cast in the slab, as well as blockouts, usually of foamed plastic, for forming openings in the finished slab.
Traditionally all of the above operations have required several workmen walking on the bed, which may be in excess of one hundred feet in length, and some eight feet or more in width. The placement of hardware on the bed is particularly time consuming and requires hauling each piece of hardware to the bed, and measuring the bed longitudinally and transversely with a tape measure or the like to locate the exact position on the bed of that particular piece of hardware.
The above operations obviously increase appreciably the production time involved as well as the labor costs necessary to produce a precast concrete slab.